= ½ dimer magnet*

A lattice of weakly interacting, antiferromagnetically coupled spin-half dimers can be well described within a Bose-Einstein condensate (BEC) of magnons model, provided the rotational symmetry of the spin Hamiltonian is preserved. The material CuVOF₄(H₂O)₆H₂O, appears to exhibit behaviour typical of a dimer system, with electron-spin resonance and magnetometry data confirming the field-induced closing of an energy-gap between the excited triplet-state and singlet ground-state energy levels. However, as the dimer-unit is composed of two unlike spin-half ions, Cu(II) and V(IV), we are presented with the interesting situation where the rotational symmetry of the system is broken by the spins in the dimer-units themselves. Here we discuss the unusual hydrogen-bond-mediated exchange pathways in this material and the resultant phase diagram. In addition, we show that the application of hydrostatic pressure serves to tune the magnitude of the intradimer exchange interaction, as well as push the system through a structural phase-transition at pressures beyond 20 kbar.